[tracing] Ignore tracing allocations in heap profiler

base/trace_event/heap_profiler.h

+// Copyright 2015 The Chromium Authors. All rights reserved.

[Dmitry Skiba, 2016/04/22 05:37:45]

2016

[ssid, 2016/04/22 05:48:27]

Done.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TRACE_EVENT_HEAP_PROFILER_H
+#define BASE_TRACE_EVENT_HEAP_PROFILER_H
+
+#include "base/trace_event/heap_profiler_allocation_context_tracker.h"
+
+// This header file defines the set of macros that are used to track memory
+// usage in the heap profiler. This is in addition to the macros defined in
+// trace_event.h and are specific to heap profiler. This file also defines
+// implementation details of these macros.
+
+// Implementation detail: heap profiler macros create temporary variables to

[Primiano Tucci (use gerrit), 2016/04/22 09:24:50]

this is really overkill, you are adding 7 lines, and you would get here the same
benefit of just doing, below in the macro

#define HEAP_PROFILER_SCOPED_IGNORE \
  trace_event_internal::HeapProfilerScopedIgnore scoped_ignore#__LINE__

which is way easier to read.

[ssid, 2016/04/22 14:49:06]

As I said in earlier mail, this doesn't work.
It prints
scoped_ignore#40.
There's no easy way  I could find to get it without 3 macros.

+// keep instrumentation overhead low. These macros give each temporary variable
+// a unique name based on the line number to prevent name collisions.
+#define INTERNAL_HEAP_PROFILER_EVENT_UID3(a, b) heap_profiler_unique_##a##b
+#define INTERNAL_HEAP_PROFILER_EVENT_UID2(a, b) \
+  INTERNAL_HEAP_PROFILER_EVENT_UID3(a, b)
+#define INTERNAL_HEAP_PROFILER_EVENT_UID(name_prefix) \
+  INTERNAL_HEAP_PROFILER_EVENT_UID2(name_prefix, __LINE__)
+
+// A scoped ignore event used to tell heap profiler to ignore all the
+// allocations in the scope. It is useful to exclude allocations made for
+// tracing from the heap profiler dumps.
+#define HEAP_PROFILER_SCOPED_IGNORE                                          \
+  trace_event_internal::HeapProfilerScopedIgnore                             \
+      INTERNAL_HEAP_PROFILER_EVENT_UID(scoped_ignore);                       \

[Dmitry Skiba, 2016/04/22 05:37:45]

Why do you need this at all, if it's only used once? Let it be
INTERNAL_HEAP_PROFILER_EVENT_UID(scoped_ignore, __LINE__), and then you'll only
need one level of indirection, i.e. EVENT_UID(a, b) -> EVENT_UID2(a, b) -> a##b

However, I'm not insisting on this. You can push as is.

[ssid, 2016/04/22 05:48:27]

Yes, but at least the user of this macro doesn't have to include a __LINE__
every time, the other parts look cleaner. More over this is same as impl of
INTERNAL_TRACE_EVENT_UID

[Dmitry Skiba, 2016/04/22 06:01:20]

Actually, wait. Why it's called INTERNAL_HEAP_PROFILER_EVENT_UID? It's not
related to any event stuff, right? INTERNAL_TRACE_EVENT_UID makes sense because
it's used in trace_event implementation. This should be just
INTERNAL_HEAP_PROFILER_UID I think.

[ssid, 2016/04/22 16:24:49]

Done.

+  if (UNLIKELY(                                                              \
+          base::trace_event::AllocationContextTracker::capture_enabled()))   \
+  base::trace_event::AllocationContextTracker::GetInstanceForCurrentThread() \
+      ->begin_ignore_scope()

[Dmitry Skiba, 2016/04/22 05:37:45]

Wait, why this is not in HeapProfilerScopedIngnore' constructor?

[ssid, 2016/04/22 05:48:27]

Primiano had suggested that keeping this out reduces a call to constructor
itself. this gets inlined.

[Dmitry Skiba, 2016/04/22 06:01:20]

How about inline constructor then? Actually, how about inlining both of them?

[Primiano Tucci (use gerrit), 2016/04/22 09:24:50]

inlining both SGTM and might be even cleaner (also you'll avoid the need of the
cc file).

[ssid, 2016/04/22 16:24:49]

Done.

+
+namespace trace_event_internal {
+
+class BASE_EXPORT HeapProfilerScopedIgnore {
+ public:
+  HeapProfilerScopedIgnore();
+  ~HeapProfilerScopedIgnore();
+};
+
+}  // namespace trace_event_internal
+
+#endif  // BASE_TRACE_EVENT_HEAP_PROFILER_H